Power supply circuits are utilized in electronic devices to provide an electronic device with continuous operation. For example, a television set utilizes a power supply circuit to provide electrical power for reception and transmission of broadcast, cable or satellite signals to a user. Many electronic devices include a standby mode which provides electrical power to the electronic device for activating such devices. Again for example, a present-day television set is equipped with a low power stand-by power supply circuit, to activate the television set and operate at times when the television set is in a power-off mode.
The stand-by power supply circuit provides electrical power to a micro-controller and infra-red receiver such that the power-on may be accomplished by a remote control at any time. Contrary to what the term “stand-by power supply” implies, the stand-by power supply circuit does not stop working when the television set is in power-on mode, the circuit also remains fully operational in power-on mode to keep delivering electrical power to the micro-controller and other digital circuits. In essence, stand-by power supply circuits provide continuous electrical power to electronic devices both in power-on and power-off modes.
Although stand-by power supply circuits produce only about one or two watts of output electrical power, the standby power supply circuits emit disproportionately large amounts of electromagnetic interference (EMI). The production of EMI from the stand-by power supply circuit constitutes one or more sources of noise and interference whose harmonic frequencies mix with those of a main power supply circuit, as well as those of deflection and other circuits. Having two or more power supply circuits located in close proximity to sensitive circuits poses serious threat of interference, for example beat noise, that degrades television picture quality and is difficult and costly to combat. As the need for higher picture quality and the regulation of power consumption increases it would be desirable to provide electronic devices that control power consumption and decrease EMI without increasing the resulting cost of the devices.